PROCEDE ET DISPOSITIF DE MESURE D'ECOULEMENT

FLOW MEASURING METHOD AND DEVICE

Abrégé français

La présente invention concerne un procédé et un dispositif de mesure d'écoulement destinés à mesurer la vitesse d'un écoulement monophase ou multiphase, tel qu'un écoulement multiphase dans un tuyau de processus etc.. Ce procédé consiste à calculer la vitesse de l'écoulement U par la simple mesure de valeurs consécutives de pression p, de température T et de vitesse acquise D, puis à calculer le changement de pression .DELTA.p, le changement de température .DELTA.T et le changement de vitesse acquise .DELTA.D. Ce dispositif comprend une sonde (1) avec un boîtier (2) comprenant des composants électroniques connectés à différents capteurs de la sonde (1). Cette sonde comprend un long tuyau (3) creux à capteur d'énergie, fixé par sa première extrémité (3A) au boîtier (2) et un tuyau (4) capteur cylindrique creux, situé dans le tuyau à capteur d'énergie (3) fixé par sa première extrémité (4A) à la première extrémité (3A) du tuyau à capteur d'énergie (3). Le tuyau capteur (4) comprend des capacités plaque (CA1, CA2, CA3, CA4) situées à l'extérieur de la seconde extrémité (4B), pouvant ainsi mesurer la conductance entre le tuyau à capteur d'énergie (3) et les capacités plaque (CA1, CA2, CA3, CA4) sur le tuyau capteur (4). Cette sonde comprend un capteur de pression et un capteur de température.

Abrégé anglais

Flow measuring method and device for measuring the velocity of a single-phase
or multi-phase flow, such as a multi-phase flow in a process pipe etc. The
method comprises calculating the flow velocity U only by measuring consecutive
values of pressure p, temperature T and momentum D, and then calculating the
change in pressure .DELTA.p, change in temperature .DELTA.T and change in
momentum .DELTA.D. The device comprises a probe (1) with a housing (2)
comprising electronic components connected to different sensors in the probe
(1). The probe comprises a long, hollow momentum tube (3), fastened by its
first end (3A) to the housing (2) and a hollow, cylindrical sensor tube (4),
located inside the momentum tube (3) fastened by its first end (4A) to the
first end (3A) of the momentum tube (3). The sensor tube (4) comprises plate
capacitors (CA1, CA2, CA3, CA4) located on the outside of the second end (B),
thereby being able to measure the conductance between the momentum tube (3)
and the plate capacitors (CA1, CA2, CA3, CA4) on the sensing tube (4). The
probe comprises a pressure sensor and a temperature sensor.

Revendications

7
What is claimed is:
1. Flow measuring method for the measurement of fluid velocity in a single-
phase or
multi-phase flow, the flow measuring method comprising:
performing two measurements of pressure p, temperature T and momentum D in the
proximity of each other and/or performing two measurements of pressure p,
temperature T
and momentum D at the same time, then
calculating the change in pressure .DELTA.p, change in temperature .DELTA.T
and change in
momentum .DELTA.D, where the method further comprises the steps of calculating
the velocity U
after the following formula:
.DELTA.D = - ~ U2.DELTA..rho.
where .DELTA..rho. is expressed as
<IMG>
where R mix is the universal gas constant.
2. The flow measuring method of claim 1, wherein the multi-phase flow is in
a process
pipe.

Description

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1
FLOW MEASURING METHOD AND DEVICE
Field of the Invention
The present invention relates to a method for measuring velocity in a single-
phase or
multi-phase flow, and a device for measuring different parameters in the flow.
Background of the Invention
Several measuring devices to measure different parameters in processes are
known,
the parameters being such as pressure, temperature, erosion, flow velocity and
flow
direction, momentum etc. Within the oil and gas industry it is especially
important to
monitor the conditions of the medium in different places in the installation;
in process
pipes, process tanks etc, thereby making initiatives possible if unforeseen or
unwanted
operation conditions should arise. A probe can be set into the process pipe
via a nipple,
then it is secured to the pipe by means of a flange on the pipe nipple.
An erosion measuring device is, for example, known from Norwegian patent
publication 176292, and will not be further described herein. Moreover, there
are several
other measuring devices available, which measure pressure and temperature.
Further, different momentum measuring devices are known, for example from
international patent application WO 95/16186 and patent publication US
4,788,869.
These momentum measuring devices are based on the movement of a long first
pipe in
relation to a second pipe placed inside the first pipe, where the movement is
caused by a
flow, which again causes a change in the distance between the first and the
second pipe.
The change in distance is measured as change in the conductance between the
first and
the second pipe so that using calibration data the actual momentum can be
measured.
Further measuring devices are nowadays used for the measurement of flow
density
based on ultra sonic waves or gamma rays. Also measuring devices are used for
the
measurement of water fraction, where the share of liquid in the flow is
measured. These
measuring devices are expensive, complex and bulky.
Patent publication US 4,419,898 relates to a method and an apparatus to
calculate the
mass flow of a fluid based on the measurement of pressure, temperature and
density of
the fluid.

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2
In a process installation there is a need for measuring several of these
parameters at
different locations. In this way there is a need for many different probes at
different
locations in order to achieve sufficient information regarding the condition
of the
installation. Both pipes with pipe nipples and the different probes are
expensive, and
maintenance is also demanding or labour and expensive. At the same time it is
a problem
that the different measurements are done at different locations in the process
pipe.
Consequently a time delay occurs between the measurement of, for example,
momentum and density, which again cause inaccurate measuring results.
It is an object of an aspect of the present invention to provide a measuring
method for
measuring flow velocity and for measuring the volume fraction of water, oil
and gas,
without firstly measuring the density of the flow. It is also an object of an
aspect of the
invention to provide a probe capable of performing the measuring method.
An object of an aspect of the invention is to provide one probe that is able
to
perform several measurements at the same location and at the same time in a
process pipe.
At the same time it is an object of an aspect of the invention to provide a
total system
that becomes less complex, with fewer pipe nipples and fewer probes. Further,
it is an
object of an aspect of the invention that the replacement of the probes and
maintenance on
the system is made easier and that the costs of accomplishing this are
reduced.
Summary of the Invention
According to one aspect of the invention there is provided a flow measuring
method
for the measurement of fluid velocity in a single-phase or multi-phase flow,
the flow
measuring method comprising:
performing two measurements of pressure p, temperature T and momentum D in
the proximity of each other and/or performing two measurements of pressure p,
temperature T and momentum D at the same time, then
calculating the change in pressure Ap, change in temperature AT and change in
momentum AD, where the method further comprises the steps of calculating the
velocity

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U after the following formula:
1
AD = --2U2Ap
where Ap is expressed as
RmixT
Ap = ___________________________________ Ap , Rmix
p2
where Rmi, is the universal gas constant.
Accordingly, the invention achieves measurement of flow velocity by means of
the
following parameters: momentum, pressure and temperature. In this way the
disadvantages
of firstly performing the flow density measurement is avoided.
According to another aspect a probe that is able to perform the method above
is
disclosed.
There is provided a flow measuring device for measuring different parameters
in a
single-phase or multi-phase flow in a process pipe or process tank or similar,
where a
probe comprises a housing in a first end and sensors in a second end, where
the housing
comprises a flange able to be fastened to a pipe nipple in the process pipe or
the process
tank, and where the housing preferably comprises electronic components
connected to the
different sensors in the probe to perform the measurements and then to
calibrate and
transfer the measured results to a central monitoring unit, where the probe
further
comprises a long, hollow momentum tube fastened by its first end to the
housing, where
the second end of the momentum tube is inserted into the process pipe or
process tank,
and where the probe further comprises a hollow cylindrical sensor tube located
inside the
momentum tube and fastened by a first end thereof to the first end of the
momentum tube,
where the sensor tube comprises plate capacitors located on the outside of the
second end,
thereby being able to measure the conductance between the momentum tube and
the plate
capacitors on the sensing tube, wherein the probe comprises a pressure sensor,
a
temperature sensor and a momentum sensor.
According to another aspect the erosion of the flow is measured with the same
probe.
Consequently the total installation can comprise fewer probes and fewer pipe
nipples,
which will reduce the total costs. The probe also makes it possible to perform
measurements at the same location and at the same time, which result in
increased

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3a
accuracy.
In addition this multi-functional probe can be combined with software-based
models
for the solution of Navier-Stokes flow equations, thereby quantifying the
volume of each
phase.
Brief Description of the Drawings
In the following, embodiments of the present invention will be described with
references to the enclosed drawings, where:
Fig. 1 shows a sectioned perspective view of a preferred embodiment according
to the
invention;
Fig. 2 shows a sectioned perspective view of the momentum tube of fig. 1;and
Fig. 3 shows a sectioned perspective view of the sensor tube of fig. 1.
Detailed Description of the Invention
A probe 1 according to a preferred embodiment of the invention is shown in
fig. 1.
The probe is comprised of a housing 2, a momentum tube 3, a sensor tube 4, an
erosion
sensor 5 and a pressure- and temperature sensing unit 7. The probe is meant to
be inserted
into a process pipe, a process tank etc. via a pipe nipple, for measurement of
different
parameters of the media in the process pipe or the process tank.
The cross section of the housing 2 is substantially annular, and it comprises
a circular
cavity 20 along the length of the housing. Further, the housing 2 comprises a
flange 21 for
fastening the probe 1 to the pipe nipple, a cover 22 to protect the cavity 20,
and a bushing
24. The housing also comprises an internal edge 25, where the sensor pipe 4 is
secured to
the housing 2.
The cover 22 is fastened to the housing 2 by means of a threaded connection
26, the
bushing 24 is similarly fastened to the cover 22. In this way, the cover 22
and the bushing
24 are providing a second barrier between the process medium and the outside.
Electrical wires 6 are guided from the sensors in a second part 1B of the
probe,
through the momentum tube 3 and the sensor tube 4 to the cavity 20 of the
housing 2,
where the necessary electronic components of the probe are located. Further
there are
electrical wires leading from the electrical components out from a first part
IA of the
probe, through the bushing 24 to a central monitoring unit or similar. The
electric
components will not be described here, since these may have several different
embodiments depending on requirements regarding which parameters are to be
measured,

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3h
and the accuracy of the measurements etc. In this embodiment the electrical
components
comprise a power supply unit, an ATMEL ATMega 128 microprocessor with
software, a
capacitor sensor amplifier, (for example QT9704B2 from Quantum Research Group
Ltd.)
among other components.
The momentum tube 3 is substantially cylindrical, and has a longitudinal
cylindrical
cavity (see fig. 2). The momentum tube 3 is preferably made as one unit. Its
first end 3A
comprises an inwardly threaded part 31, inwardly conic parts 32 and an
external collar 33.
In its second end 3B the momentum tube 3 comprises an inwardly cylindrical
surface 34
and an inwardly threaded part 35. The momentum tube is preferably made of an
electrically
conducting and corrosion resistant material.
The sensor tube is also substantially cylindrical, and has a longitudinal
cylindrical cavity
41 for electric wires 6 (see fig. 3). Further, in its first end 4A the sensor
tube 4 comprises a

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4
flange 42 for fastening to the internal edge 25 in the housing 2 by means of
adjusting
screws 43, and an outwardly threaded part 47. In a second end 4B the sensor
tube 4
comprises an outwardly cylindrical part 44 of an electric isolating material,
where four
plate capacitors CA1, CA2, CA3, CA4 are located outside the cylindrical part
44, the
capacitors being connected to the electrical components in the housing 2. On
the
longitudinal, central part the sensor tube comprises an external rubber packer
45, which at
the first end 4a has circular, externally conical parts 46.
The assembly of the housing 2, the momentum tube 3 and the sensor tube 4 will
now be
described. The first end 3A of the momentum tube 3 is firstly inserted into
the cavity 20,
such that the external collar 33 is supported against an area of the flange
21. From the
opposite side of the housing 2 the second end 4B of the sensor tube 4 is
inserted through
the cavity 20 through the first end of the momentum tube 3, and the outwardly
threaded
part 7 of the sensor tube 4 is screwed onto the inwardly threaded part 31 of
the momentum
tube 3.
The momentum tube 3 may comprise a radially located latch pin to lock the
momentum
tube 3 and the sensor tube 4 in relation to each other, thereby preventing any
rotation of the
sensors in the other part 1B of the probe relative to the wanted direction.
In this position the exterior conical part 46 of the sensor tube is supported
against the
interior conical parts 32 of the momentum tube, and at the same time the
cylindrical part 44
of the sensor tube, comprising the plate capacitors CA1, CA2, CA3, CA4, is
located inside
of and radially at a distance from the inner cylindrical surface 34 of the
momentum tube.
The exterior flange 42 is then fastened to the inner edge 25 of the housing 2
by means of
the adjustment screws 43. The area between the exterior collar 33 and the
flange 21 is
welded. The sensor is connected to the electrical components which is located
in the cavity
20. The cover is put on, and finally the area between the housing 2 and the
cover 22 is
welded.
Dependant on the parameters to be measured, additional sensor units are placed
on the
other end 3B of the momentum tube. Preferably additional sensor units have
outwardly
directed threads adapted to the inwardly threaded part 35. When the sensor
units are
screwed in, the area between the momentum tube and the sensor tube is welded.
Two
different alternatives will be described in the following.
In a simple embodiment a pressure and temperature unit (not shown) are
inserted into the
momentum tube. The pressure and temperature unit comprises for example a
circular or
disk-shaped pressure and temperature sensor inserted into or welded into the
substance of
the unit. The pressure and temperature sensor can, for example, be a
piezoelectric unit with
its own separation membrane for pressure transfer.

CA 02511748 2011-12-02
In a preferred embodiment the probe 1 comprises an additional erosion sensor
5, known
per se. The erosion sensor 5 comprises an outwardly threaded part adapted to
the inwardly
threaded part 35, where the electric wires 6 conduct signals to the electric
components. The
pressure and temperature unit 7 here, for example, is integrated as a part of
the erosion
5 sensor 5, as shown in fig. 1.
The momentum measurement will in the following be described briefly, since it
is
basically known from the publications cited above. The momentum tube 3 forms
the
flexible part during the momentum measurement. When the flow generates an
input to the
probe, the second part 3B of the momentum tube 3 will be deflected a small
distance, and
the capacitance between the conductor plates CA1, CA2, CA3, CA4 on the sensing
tube 4
and the inner cylindrical surface 34 of the momentum tube will be measured by
the
electronic components in the housing 2. The capacitance is then compared to
measurements performed during calibration, and the momentum is calculated.
The fluid velocity can be calculated from the following equations as functions
of
momentum, temperature and pressure, that is, without having to firstly measure
the density.
RT
P = __________________________________________________________ (1)
Here, Rm,õ is the universal gas constant, T is temperature and p is pressure.
Differentiating equation (1) results in:
RmixT
Ap + Rin`x AT (2)
p2
Here, Ap is change in density, AT is change in temperature, and Ap is change
in pressure.
Two previous measurements are now used to derive the change in velocity AU
from equation (2).
By using the principle of continuity the change in velocity AU can be
expressed by

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5a
the change in density A p, and vice versa:
pU =(p+ Ap)(U + AU)
AU = ¨OP- (3)
Finally, the impulse equation is used, resulting in:
D = cp -21pU2 (4)
1
AD = pU AU + ¨2 pU2 Ap
Here, D is an expression of the measured momentum, AD is change in measured
momentum, while CD is the momentum coefficient depending on the area of the
probe, the
shape of the probe etc.
The following expression is achieved by replacing AU in equation (3):
AD = ¨U2Ap + U2Ap = U2Ap (5)
2 2
We now find the velocity U from the change in momentum AD, where Ap is a
function
of the measured values for AT, T, Ap and p in equation (2).
The accuracy in the method is very dependent on the quality of the measured
pressure,
temperature and momentum parameters. This type of analysis will provide the
necessary
quality and the required accuracy.
It is further possible to connect other known sensor units between the
momentum tube 3
and the erosion sensor 5, or possibly between the momentum tube 3 and the
pressure and
temperature unit.

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We now find the velocity U from the change in momentum AD, where Ap is a
function of
the measured values for AT, T, Ap and p in equation (2).
The accuracy in the method is very dependant on the quality of the measured
pressure,
temperature and momentum parameters. This type of analysis will provide the
necessary
quality and the required accuracy.
It is further possible to connect other known sensor units between the
momentum tube 3
and the erosion sensor 5, or possibly between the momentum tube 3 and the
pressure and
temperature unit.

Dessin représentatif